Searcharxiv⌕ Search

arXiv subjects

S. S. Afonin

Publications and source records attributed to S. S. Afonin.

At least 73 records · Page 4Linked to original sources
arXiv2009

Regge spectrum from holographic models inspired by OPE

The problem of obtaining the Regge-like behaviour for meson mass spectrum in the hard-wall AdS/QCD models is addressed. We show that the problem can be solved by a simple incorporation of the effects of local vacuum condensates into such models. The slope of trajectories turns out to be determined by the local condensate of dimension~2 that is absent in the standard Operator Product Expansion. This pitfall, however, can be escaped by means of physically plausible modification of boundary conditions for the holographic fields corresponding to the usual gluon condensate, the latter then determines the slope.

hep-ph↗
arXiv2009

Note on description of excited hadrons with fixed angular momentum

In this Note, we make comments on the recent criticism of the description of highly excited hadrons in terms of fixed angular momentum L and quantify the relation M^2\sim L+n+S/2 (n is the radial quantum number and S is the total quark spin) for masses of light mesons.

hep-ph↗
arXiv2009

About the possibility of five-dimensional effective theories for low-energy QCD

The AdS/QCD models suggest an interesting idea that the effective theory of low-energy QCD may be formulated as a 5-dimensional field theory in the weak coupling regime in which the fifth coordinate plays a role of inverse energy scale. Taking the point of view that this is just an efficient parametrization of the non-perturbative dynamics of strong interactions, we discuss on a qualitative level an alternative possibility for a simpler 5-dimensional parametrization of main phenomena in the low-energy QCD. We propose to interpret the effect of chiral symmetry breaking as an effective appearance of compactified extra dimension with the radius of the order of inverse scale of chiral symmetry breaking. Following some heuristic arguments two dual scenarios for the emergence of the excited light mesons are introduced: In the first scenario, the meson resonances are interpreted as the effects of Kaluza-Klein excitations of quarks inside mesons, in the second one, as the formation of gluon strings wound around the compactified dimension an appropriate number of times. Matching of these scenarios permits to express the slope of radial Regge trajectories through the order parameters of the chiral symmetry breaking, with the compactification radius being excluded. This example shows qualitatively that the extra dimension may play an auxiliary role providing a short way for deriving new relations.

hep-ph↗
arXiv2009

AdS/QCD models describing a finite number of excited mesons with Regge spectrum

The typical AdS/QCD models deal with the large-N_c limit of QCD, as a consequence the meson spectrum consists of the infinite number of states that is far from the real situation. Basing on introduction of anharmonic corrections to the holographic potential, the corrections whose existence has been recently advocated, we construct a class of bottom-up holographic models describing arbitrary finite number of states in the sector of light mesons. Within the proposed approach, the spectrum of masses square has the following properties: It is linear, $m_n^2\sim n$, at not very large n, nonlinear at larger n, with the nonlinear corrections being subleading in 1/N_c, has a limiting mass, and the number of states is proportional to N_c. The considered holographic models reflect thereby the merging of resonances into continuum and the breaking of gluon string at sufficiently large quark-antiquark separation that causes the linear Regge trajectories to bend down. We show that these models provide a correct description for the spectrum of excited rho-mesons.

hep-ph↗
arXiv2008

Implications of the Crystal Barrel data for meson-baryon symmetries

Making use of numerous resonances discovered by the Crystal Barrel Collaboration we discuss some possible relations between the baryon and meson spectra of resonances composed of the light non-strange quarks. Our goal is to indicate new features that should be reproduced by the realistic dynamical models describing the hadron spectrum in the sector of light quarks.

hep-ph↗
arXiv2008

Hydrogen like classification for light nonstrange mesons

The recent experimental results on the spectrum of highly excited light nonstrange mesons are known to reveal a high degree of degeneracy among different groups of states. We revise some suggestions about the nature of the phenomenon and put the relevant ideas into the final shape. The full group of approximate mass degeneracies is argued to be $SU(2)_f\times I\times O(4)$, where $I$ is the degeneracy of isosinglets and isotriplets and O(4) is the degeneracy group of the relativistic hydrogen atom. We discuss the dynamical origin and consequences of considered symmetry with a special emphasis on distinctions of this symmetry from the so-called chiral symmetry restoration scenario.

hep-ph↗
arXiv2008

Axial coupling from matching constituent quark model to QCD

The axial-vector coupling $g_A$ of a constituent quark is estimated from matching the constituent quark model to the operator product expansion in QCD in the limit of large number of colours under some assumptions. The obtained relation is $g_A\simeq\sqrt{7/11}\approx0.80$, which is in agreement with the existing model estimates.

hep-ph↗
arXiv2007

Illustrative Model for Parity Doubling of Energy Levels

A one-dimensional quantum mechanical model possessing mass gap, a gapless excitation, and an approximate parity doubling of energy levels is constructed basing on heuristic QCD-inspired arguments. The model may serve for illustrative purposes in considering the related dynamical phenomena in particle and nuclear physics.

hep-ph↗
arXiv2007

Weinberg like sum rules revisited

The generalized Weinberg sum rules containing the difference of isovector vector and axial-vector spectral functions saturated by both finite and infinite number of narrow resonances are considered. We summarize the status of these sum rules and analyze their overall agreement with phenomenological Lagrangians, low-energy relations, parity doubling, hadron string models, and experimental data.

hep-ph↗
arXiv2007

Spontaneous P-parity violation in dense baryon matter

We investigate possibilities for dynamical P-parity violation in dense baryon matter in the framework of effective quark models. Dynamical P-parity violation can appear in models with at least two scalar and two pseudoscalar fields, where both scalar fields are condensed at normal conditions. At special configurations of coupling constants, one of pseudoscalar fields can then also condense at some value of baryon density, the phenomenon results in mixing of the scalar and pseudoscalar physical degrees of freedom, hence, giving rise to P-parity violation. We discuss the implications and possible experimental signatures for P-parity violation in strong interactions in future experiments with heavy-ion collisions.

hep-ph↗
arXiv2007

Parity doubling in particle physics

Parity doubling in excited hadrons is reviewed. Parity degeneracy in hadrons was first experimentally observed 40 years ago. Recently new experimental data on light mesons caused much excitement and renewed interest to the phenomenon, which still remains to be enigmatic. The present retrospective review is an attempt to trace the history of parity doubling phenomenon, thus providing a kind of introduction to the subject. We begin with early approaches of 1960s (Regge theory and dynamical symmetries) and end up with the latest trends (manifestations of broader degeneracies and AdS/QCD). We show the evolution of various ideas about parity doubling. The experimental evidence for this phenomenon is scrutinized in the non-strange sector. Some experiments of 1960s devoted to the search for missing non-strange bosons are re-examined and it is argued that results of these experiments are encouraging from the modern perspective.

hep-ph↗
arXiv2007

Towards understanding broad degeneracy in non-strange mesons

The spectroscopic regularities of modern empirical data on the non-strange mesons up to 2.4 GeV can be summarized as a systematic clustering of states near certain values of energy. It is getting evident that some unknown X-symmetry triggers the phenomenon. We review the experimental status of this symmetry and recent theoretical attempts put forward for explanation of broad degeneracy.

hep-ph↗
arXiv2007

Properties of new unflavored mesons below 2.4 GeV

The global features of spectrum of highly excited light nonstrange mesons can be well understood within both chiral symmetry restoration scenario combined with the relation $M^2\sim J+n$ and within nonrelativistic description based on the relation $M^2\sim L+n$. The predictions of these two alternative classifications for missing states are different and only future experiments can distinguish between the two. We elaborate and compare systematically the predictions of both schemes, which may serve as a suggestion for future experiments devoted to the search for missing states.

hep-ph↗
arXiv2007

Cluster duality

It is well known that the linear mass spectrum of light mesons in the large-N_c limit is dual to the perturbative QCD continuum. We find the form of the linear spectrum which is maximally dual to the perturbation theory. The obtained ansatz turns out to be the spectrum of the Lovelace-Shapiro dual amplitude. This spectrum is chirally symmetric in the sense that it corresponds to zero values for the order parameters of chiral symmetry breaking in QCD. We further assume that the actual spectrum is dual to the maximally dual one within the QCD sum rules based on OPE and in this way recover some known important relations and statements. The experimental spectrum seems to support the assumed duality: The masses of resonances cluster near certain equidistant values of energy squared and the positions of clustering follow the maximally dual ansatz. The latter fact signals the chiral symmetry restoration in the excited states. We discuss also two topics of recent interest: nonlinear corrections to the string-like spectrum and the dimension-two gluon condensate.

hep-ph↗
arXiv2006

Qualitative solution of QCD sum rules

We show how such important features of QCD as chiral symmetry breaking or the formation of a mass-gap can be directly traced from QCD sum rules for two point functions assuming, in the large number of colors limit, exact duality between the operator product expansion and the spectrum described by linearly (or nearly linear) rising Regge trajectories as predicted by string theory. We see how the presence of chiral symmetry breaking is intimately related to confinement in this scenario, as expected from general arguments, and how Regge trajectories change when chiral symmetry is broken. As a result the whole meson mass spectrum can be parametrized with a good accuracy by the constant $f_π$ only, thus realizing the program proposed by Migdal some time ago.

hep-ph↗
arXiv2006

Light meson spectrum and classical symmetries of QCD

Modern spectroscopic data on light non-strange meson spectrum is analyzed. It is argued that the observed regularities of experimental spectrum for highly excited states favour a partial restoration of all approximate classical symmetries of QCD Lagrangian (conformal, chiral and axial) broken by the quantum corrections. The rate of restoration of classical symmetries is estimated. The dependence of the resonance widths from the corresponding masses is systematically checked. On average, it turns out to be universal for the high excitations as predicted by the effective string description.

hep-ph↗
arXiv2006

Experimental indication on chiral symmetry restoration in meson spectrum

The spectroscopic predictions of the Ademollo-Veneziano-Weinberg dual model are critically tested in view of the modern experimental data. The predicted equidistance of masses squared for chiral partners is shown to be violated high in energies, instead one observes an approximate degeneracy of these quantities. This phenomenon can be interpreted as the restoration of Wigner-Weyl realization of chiral symmetry for highly excited states. The scale of complete restoration is expected to be 2.5 GeV. A multispin-parity cluster structure of meson spectrum is revealed.

hep-ph↗